We are interested in studying multigenic families, and are studying three systems: 1. Antibodies are coded by three families of genes--lambda, kappa, and H. Each family is generally multigenic. The multigenic antibody families display unusual evolutionary features which suggest the presence of novel evolutionary mechanisms as well as unusual genetic features which suggest that gene translocation plays a role in the differentiation of the antibody-producing cell. The genetic basis for antibody diversity, evolution, and expression will be studied through the comparative amino acid sequence analysis of immunoglobulins derived from selected vertebrates--primarily the NZB mouse, the rabbit and the pigeon. 2. We also are studying the structure of the receptor IgM molecule on mouse B cells (tumor and normal). We have recently completed the entire amino acid sequence of a soluble mouse micron chain (MOPC104E). We plan to do a detailed comparison of the structures of the membrane-bound and soluble micron chains. 3. We are studying Ia molecules from rat, mouse, and guinea pig. These membrane molecules are encoded by one or more multigenic families lying in the major histocompatibility complex of mammals. Their diversity, regulation, evolution and gene organization will be compared with those of their immunoglobulin counterparts.